88 MICROBES, FERMENTS, AND MOULDS. 



putrefaction. Those which are dead appear as small, 

 rigid, and immovable rods. 



In observing the lively movements of these minute 

 organisms, we might be tempted to regard them as 

 animals. But we know that movement, taken by 

 itself, is not peculiar to the animal kingdom. Setting 

 aside the movement which can be provoked in the 

 mimosa and in many higher plants, it is well to 

 remember that many of the lower plants are capable 

 of motion : this is the case with BiatomacecB, in which 

 the presence of chlorophyl incontestably proves their 

 vegetable nature. The spores of plants of a much 

 higher organization, such as ferns and mosses, have the 

 power of swimming in the water, just as bacteria have : 

 this has procured for them the name of Zoospores, 

 although many of them contain chlorophyl. 



The movements of bacteria are, like those of zoo- 

 spores, due to the presence of vibrating cilia, which 

 are inserted at both extremities, or only at the hinder 

 extremity of the microbe, and which form organs of 

 propulsion analogous to the tails of tadpoles. These 

 organs are very transparent and are difficult to see in 

 the living subject, even with the strongest magnifying 

 power, on account of the rapidity of their movements. 

 But their existence has been ascertained by the use of 

 staining fluids, and above all by micro-photography. 



If, however, we analyze the mode of motion in 

 Bacterium termo, and compare it with the movements 

 of the ciliated or flagellated infusoria which may often 



